Acoustic chamber



Nov. 17, 1931. wAM. CAMPBELL ACOUSTIC CHAMBER Original Filed Sept. 26,

Patented Nov. 17, 1931 UNITED STATES PATENT OFFICE 5 WILLIAM 1r. CAMPBELL, or NORTH, VANCOUVER, BRITISH COLUMBIA, CANADA w ACOUSTIC CHAMBER Application filed september 26, 1927, Serial No. 222,122. Renewed December "12,1929.

This invention relates to acoustic devices and more particularly to sound amplifiers of that type generally employed in connection with phonographs or 'gramophones, radios 5 and the like, the principal object being to reproduce and amplify sounds of all characters without distortion. v Y

I-Ieretofore in the use of tone arms, sound boxes and like instruments any turns that 1 were made were on the arc of a circle so that the sound waves from a diaphragm or other source impinging against the arc were deflected at many different angles and then from side to side in a forward direction pro- 1 ducing cross reflections which interfered with each other and absorbed acoustic energy so that the sound emitted from the device was considerably distorted particularlyas to the lower frequencies or bass notes althoughthe higher frequencies were also considerably impaired.

Itis therefore the object of this invention to avoid these defects and obvious faults and broadly speaking consists in reflecting or de- 2 flecting the sound waves in straight lines and in the axis of the tubular section through which they are to pass so that cross reflections are obviated and there is substantially no impingement of the waves against the side wells of the tubular sections.

a The principle simply explained is the use of substantially optically flat reflecting surfaces arranged at suitable angles so that a F wave of sound may be transmitted without 3 distortion; and in its course duly amplified also without distortion.

A still further object is the provision of a sound amplifyingjchamber which maybe conveniently and economically constructed 40 and which is extremely compact, adapted to maintain a the advancing wave front of the sound vibrations in a planeapproximately at right angles to the axis of the conduit.

Further objects of the, invention will appear as'the following specific description is read in connection with the drawings which form part of this application and in which:

Figure 1 is a front elevation;

Figure 2 is a vertical section on the line A-B of Figure 1;

Figure 3 is a horizontal) section on the line C-D of Figure 1; p

Figure 4cis a vertical section on the line EF of Figure 3; and, a

Figure 5 is a vertical sectional view taken on the line GI-I of Figure 4.: a p In the specificembodiment which I have llustrated herein for the purpose of explaining my invention I provide two-side membersa and 6 connected together and held in spaced relation by end members 0 and d and bottom and top members e and f all of which may be constructed of any suitablematerial but whichare preferably made of wood. As

shown the bottom members 6 and the end members 0 and are connected together by angular corner pieces 9 while the end members 0 and d are connected to the top members f by means of similar angular corner pieces a. In the center between the s de pieces a and b, I extend inwardly from top toward the bottom two partition members i and t which form a tube 15 terminating short of the bottom" as shown in Figures l and 4 and within, this tube I insert a flaring throat member 9 provided with a flange 10 at its upper end resting upon the upper edges of the partitions 2' and z" and upon the upper edges of thevsidef members a and b. The tubeconsistin g of the side members wand b and the part tions i and 2" 1s connected to the top members f by angular pieces f corresponding to the angular pieces and lying in planes parallel to the angular p eces 9.

, To the lower end of the tube 15" and extending between the side plates a and b are horizontal plates 72 and spaced'from the part t ons i and i on either side are short partitlons Z which connect at their lower ends with the plates is andterminate short of the top plates f. Between these partitions ;Z and in the axis of the throat tube 9 so that sound waves passing through said throat tube will be divided at 8 and impinge against the opposite surfaces 10 and be directed at substantial right angles to their line of entrance.

In the operation of the device sound entering the throat tube 9 at the entrance 6 will divide at 8 impinging against the opposite angular surfaces 10 and be directed in a straight line in opposite directions to the surfaces 11 where they will be again reflected at substantial right angles and will in turn impinge upon the surface 12, 13 and 1a where they emerge through the opening 7 and can be further amplified if desired by connecting the present device with a horn.

It will be noted that the oppositely directed channels indicated at 16, 17, 18 and 19 all increase in size from the point where sound enters each channel to the point where it emerges therefrom and in order to accomplish this in the channels 16 I have made the plates 7c thinner at one side than at the other while in the channel 17 the partition members Z have been inclined away from the side plates 0 and d. This inclination to widen the channels from their entrance points 20 to their exit points causes a restriction at the upper or entrance end of the channel 19 and an enlargement of the same channel at the point of emergence of the sound waves there from.

By constructing the device in the manner above described it will be seen that I have completely avoided the bad features of curved surfaces and insure a PI'OJGCtlOD of the sound waves in straight lines without any substantial contact with the side walls of the respective channels thereby avoiding cross reflections and consequent distortion for it will of course berealized that if the surfaces 10, 11, 12, 13 and 14 were curved surfaces sound waves would be deflected against the inner surfaces of the end and side plates and cross reflections would develop between the bottom plates 0 and cl and the top plates 7 and between the partition members 2' and i and the partitions Z. With the angular surfaces the wave passes in substantially straight lines through the channels 16, 17, 18

and 19 with the wave front substantially perpepdicular with the wall defining these channe s.

Having now particularly described my invention, what I claim as my invention and desire to be protected in by Letters Patent is 1. An acoustic chamber for a sound amplifying device comprising, a rectangular tube of gradually increasing area, said tube branching symmetrically to form two approximately spiral convolutions, the inner wall of said convolutions being common thus affording a maximum of compactness, said spiral form being obtained by angular inclinations of said tubes at forty-five degrees, the intake aperture of said chamber being right-angular to its outlets.

2. An acoustic chamber for a sound amplifying device comprising, a tube of rectangular cross section formed by division walls right-angular to and secured between two flat sided members which are parallel to each other, said tube having its intake central to and located between the two said parallel members and having its outlet at right angles toits intake and to the said flat sided members, said central intake bifurcating to form two symmetrical and approximately spiral right and left handed convolutions of rectangular tubes, each said tube being in form folded upon itself with its inner walls in contiguity so that adjacent convolutions are separated only by the thickness of a wall,

the general form of the said approximate spiral being that of an irregular octagon and the change of direction in the said tubes necessary to form the said approximate spiral being by angular inclinations.

3. An acoustic chamber for a sound amplifying device comprising, a tube of rectangular cross section formed by division walls rigl'it-angular to and secured between two flat sided members which. are parallel to each other, said tube having its intake central to and located between the two said parallel members and having its outlet at right angles to its intake and to the said flat sided members, said central intake bifurcating to form two symmetrical and approximately spiral right and left handed convolutions of rectangular tubes, each said tube being in form folded upon itself with its inner walls in contiguity so that adjacent convolutions are separated, only by the thickness of a wall, the. general form of the said approximate spiral being that of an irregularoctagon and the change of direction in the said tubes necessary to form the said approximate spiral being by angular inclinations, a separate throat member comprising a circular tube gradually changing to one of rectangular and increasing cross section, said tube having a flange at its intake aperture.

l. An acoustic chamber for a sound amplifying device comprising, an open-ended tube having its transverse area gradually increasing from its intake end, said tube branching symmetrically right and left handedly to form the exterior members of two convolutionshaving an approximately spiral character, said approximate spiral being obtained by angular inclinations of said tubes, the single intake aperture of said chamber being right-angular to its double tube outlet.

5. An acoustic chamber for sound amplifying devices comprising a tube bent angularly in substantially U-shape formation and having an inner wall forming a common dividing wall bet-ween the two legs of said tube, the walls of said tube at their points of angularity being disposed in flat uninterrupted planes at angles of 45 to the axis of the legs, thereby projecting sound. waves passing through said legs in opposite directions and parallel to each other on opposite sides of the common wall.

In testimony whereof I aflix my signature. WILLIAM M. GAMBBELL. e 

